1. Field of the Invention
The invention relates in general to a prosthetic eye and, more particularly, to an ocular prosthesis and a process of fabrication of the same.
2. Description of the Related Art
It is not uncommon for a person to have a natural eye removed because of a severe trauma, a congenital abnormality, or a disease, such as, for example, an infection, the presence of a tumor, or untreatable painful glaucoma. In these situations, the natural eye is removed by an acceptable medical procedure, for example, by enucleation or evisceration, during which a orbital implant is surgically implanted to replace lost orbital volume. It is also not uncommon for a person to have a smaller than normal, or phthisical eye, that is blind. In order to restore the person to a more normal anatomical structure and restore the cosmetic defect created by these conditions an ocular prosthesis is created. The initial step in creating this prosthesis is the taking of an impression of the ocular socket. From that impression, an ocular prosthesis simulating the person's natural eye is created and inserted into the ocular socket posterior to the lids and anterior to the orbital implant or phthisical globe. With such a procedure, a person's psychological trauma associated with the eye loss is reduced, and a more cosmetically acceptable appearance results from the use of the prosthesis. FIG. 1 illustrates a generic ocular prosthesis 10. As shown, these prostheses usually comprise a scleral region 20 with veins 30, an iris 40, a pupil 50 and a clear corneal layer (not illustrated).
Although several improvements have been reported in the general art of ocular prosthesis, fabrication methods currently used are based upon outdated technology, are cumbersome, lack a high degree of precision, and are time consuming, as further explained below. Examples of improvements in the art include a method of magnetically coupling a prosthesis with an ocular implant described by Garonzik in U.S. Pat. No. 6,530,953 designed to eliminate the use of a coupling post in the integration process of the prosthesis with the ocular implant. Kelley, in U.S. Pat. No. 5,171,265, discloses a self-lubricating ocular prosthesis designed to dispense a lubricating fluid by use of a dispensing ball or a button that can be depressed on demand. U.S. Pat. No. 4,332,039, issued on Jun. 1, 1982 to Henry LaFuente, discloses an ocular prosthesis having a pupil that changes in diameter to simulate the behavior of a natural eye when exposed to light of varying intensity. The U.S. Patent to Schleipman et al. (U.S. Pat. No. 6,391,057) discloses a prosthesis with similar characteristics to the one disclosed by LaFuente; while Friel, in U.S. Pat. No. 5,061,279, disclosed an ocular prosthesis capable of simulating human pupil dilation by the use of photochromic pigments that changes the density of their color in response to differing wavelengths of light from clear to opaque. Finally, in U.S. Pat. No. 5,326,346, Cortes discloses an ocular prosthesis made of light-cured urethane dimethacrylate, thus minimizing allergic reactions by the user of the prosthesis by essentially eliminating any residual monomers.
However, despite the above-noted exemplary improvements, conventional fabrication methods produce ocular prosthetics whose shapes are usually inaccurate and difficult to reproduce, are time consuming, employ materials and methods of curing the materials that have the potential to cause undesirable allergic reactions, and are labor intensive.
Conventional processes that are currently used to produce ocular prosthetics have been around for more than sixty years. They traditionally begin with the taking of an impression of the anophthalmic or enophthalmic eye socket in a process similar to that of taking a dental impression. First a conforming impression tray is selected and placed into the socket anterior to the globe or implant and posterior to the lids. An impression material is then introduced into the eye socket via a tube protruding from the anterior surface of the impression tray and projecting out between the lids by means of a syringe connected to the tube. After the impression material has set, the impression is removed and invested in dental gypsum in order to obtain a positive cast of the posterior aspect of the eye socket.
Subsequently, the gypsum cast is coated with a separating medium and either dental base plate wax or inlay wax is then shaped thereon in an empirical approximation of the anterior curves of the wax form that will comprise the form for investment. These anterior curves and the posterior surface of the wax are modified in order to achieve patient comfort, appropriate anterior/posterior dimension, palpebral fissure curvature, and iris center position. The iris center position is then identified with a screw coated in wax or an iris peg that identifies the iris center and plane. Because of the empirical nature of this portion of the conventional fabrication processes, an undesirable variation in the accuracy of the shape occurs.
Once the wax investment form is finished, a two part mold is made of the prototype ocular prosthesis using dental gypsum within a stainless steel or brass flask. The anterior portion of the mold is invested, a separating medium is applied, and the posterior portion of the mold is invested. After the mold sections have set, the flask is opened and the wax form and iris center are removed from the mold.
In the most common form of iris duplication, the iris is painted using a viscous monomer-polymer solution and dry artist's pigments onto a Poly Methyl Methacrylate Acrylic, or PMMA disc. A PMMA corneal-pupil piece (CPP) that approximates the clear cornea is then adhered to the painted surface with a viscous monomer-polymer solution. In other forms of the process, the iris is painted on a thin sheet of tin foil placed over the convex side of a steel die which is then cured with PMMA in order to form the CCP, or the iris is painted in the appropriate location on a slightly convex anterior surface of the white portion of the prosthesis. The problems associated with hand painted irises include the inherent inaccuracy of hand painting and the fact that only a limited three-dimensional depth effect can be portrayed.
When forming the white posterior section of the prosthesis, the above-summarized, two-part mold is cleaned and inspected and a liquid separator is applied to each gypsum section. The corneal-pupil-iris piece (CPIP) is then placed into its pre-determined location in the mold anterior section. PMMA powder that has had intrinsic pigments added in order to replicate the base colors of the natural sclera of the eye is then mixed with PMMA monomer. This mixture is allowed to polymerize until it reaches a consistency that pulls apart with a snap. The polymerized scleral acrylic mixture is packed into the anterior mold section to overflow and the posterior section of the mold is then placed onto the anterior portion thereof. The mold is then placed in a mechanical or hydraulic press and the excess PMMA is pressed out and the mold is then placed in a curing device and heat alone or heat and or pressure are applied until polymerization has been completed. Because the amount of undesirable monomers that may remain in the prosthesis, the curing process requires long curing times. It is also not practical to destructively test the material once cured in order to ensure proper polymerization as the batch size is necessarily small, then the prosthesis itself would be destroyed. After curing, the scleral portion of the prosthesis is removed from the mould, parting line flash is ground away, the corneal area is reduced until the iris is exposed to a desired diameter, and the anterior-posterior surface of the scleral area is reduced by hand.
Subsequently, iris tones are next enhanced over the CPIP, or applied to the anterior surface. The colors of the sclera are duplicated on the surface and silk fibers are added to duplicate the veining patterns of the contra-lateral eye. The prosthesis is then placed in a drying oven to prepare it for the placement of a clear acrylic over the anterior surface. The mold is again inspected, repaired, and a liquid separator is applied to both gypsum sections in preparation for the application of a clear capping. Clear PMMA polymer and monomer are mixed and polymerized until reaching the same snappy state as previously described. The clear acrylic is then placed on the anterior surface of the painted section and the anterior and posterior flask sections are closed and the excess acrylic is pressed out. Polymerization and cooling as previously described follow. The same material concerns as previously described apply to this process of polymerization.
Finally, the prosthesis is removed from the mold, parting line flash and surface irregularities caused by latent air bubbles or other defects in the mould are then ground away, and the surfaces are smoothed with a fine hand piece burr. The prosthesis is then smoothed with a paste of medium flour of pumice and water. Progressively finer abrasives are used until all surfaces are smooth and show no scratches under ten times magnification. The prosthesis is given a final inspection, is cleaned and disinfected and prepared for delivery to the patient.
Based at least on the foregoing summarized discussion and the exemplary problems identified with conventional methods to fabricate ocular prostheses, a need exists for an advanced ocular prosthesis and an advanced method of fabrication of an ocular prosthesis having several unique capabilities, including, as non-limiting examples: (1) improved shape accuracy through the use of both the anterior and posterior aspects of the initial impression of the ocular socket; (2) allowance for accurate and repeatable shape modification; (3) elimination of several fabrication steps by providing a way for the retention of a computerized record of an accurate shape of the ocular prosthesis; 4) use of materials that contain no methyl methacrylate monomer, or that have been tested in a manufacturing facility and proven to contain only acceptably low levels of methyl methacrylate monomer, thus possibly reducing the potential for patient allergic reactions; (5) reduction in the time necessary to create the final product; (6) automation of what has in the past been a “hand made” technique, as just explained; (7) a more realistic portray of a person's natural iris; and (8) allowance for the placement in the prosthesis of advanced technology devices, such as a retinal chip, in view of the precise ability to machine the ocular prosthesis.